RFR: 8223498: Add Sum of Duration to the jfr summary command

[Chihiro Ito]

Hi,

Could you review this enhancement, please?

This enhancement adds the total duration of each event to the jfr 
summary command to help the user determine which events to display in 
the jfr output.

webrev:
http://cr.openjdk.java.net/~cito/JDK-8223498/webrev.00/ 
<http://cr.openjdk.java.net/%7Ecito/JDK-8223498/webrev.00/>

jbs:
https://bugs.openjdk.java.net/browse/JDK-8223498

I have passed the tests in test/jdk/jdk/jfr.

Best regards,
Chihiro